South32 won approval for two more 305 metre-wide longwalls at its Dendrobium mine, extracting coal from underneath the Metropolitan Special Area which was created to protect the waters of the Avon, Cataract, Cordeaux and Nepean reservoirs.

The company, which was spun out of BHP Billiton, hailed the go-ahead as securing as many as 400 jobs. The coking coal produced at the mine supplies a steel mine in nearby Wollongong and export markets. 

Still, the two new longwalls can only be cut to a height of 3.9 metres compared with the 4.6 metres permitted for the current five longwalls in a bid to reduce the disruption to surface and groundwater from expected subsidence.

Approval was granted despite South32 commissioning a report on groundwater impacts in 2012 – when it was seeking the go-ahead for the five excavation lines – but then declining to make the findings available even to the government.

The nod for the latest expansion also came even though the Planning Department hired an independent expert to review methods for estimating the height of so-called drainage zones above coal extractions, but is yet to get the results. The drainage zone is the area above an extraction where water drains relatively freely towards the mine.

"Due to the complexity of the issues and the significant amount of work required, this report is now not expected to be finalised and peer reviewed until early 2017," a Planning spokeswoman told Fairfax Media.

(Image above: Cracked and drained Wongawilli Creek tributary in Special Areas. (Supplied.))

Water loss

In a report sent to Planning Minister Rob Stokes, just before the latest approval, the NSW National Parks Association (NPA) estimated 29-40 million litres a day of water were entering the coal mines in and around the Illawarra Special Areas, including Dendrobium.

(See map below of the Wongawilli (lower mines) and Dendrobium coal mines (upper set) sprawling between the Avon and Cordeaux Reservoirs.)

According to the NPA, the mid-range estimate is equivalent to about 10 per cent of the total daily supply taken from the Avon, Cataract, Cordeaux, and Woronora reservoirs.

"It's important to note that there is currently no reliable means of knowing how much of this water would have otherwise gone into the storage reservoirs", Peter Turner, NPA mining projects officer, said.

Those estimates, though, may be conservative because they don't include inflows that are adding to water bodies accumulating within the mines, Dr Turner said.

"There doesn't appear to be any reporting or auditing of water pooling," he said. "It's not clear whether the Dendrobium and adjacent Wongawilli mines are staying within their water licence limits."

A spokesman for South32 said groundwater assessments at the mine were "comprehensive and ongoing".

"We submit reports to government, but the publishing of those reports is a matter for the government," he said, adding the 2012 report sought by the NPA and Planning "was never finalised".

"A report was produced, which satisfies the condition of approval for Dendrobium Area 3B [the expansion zone including the seven longwalls], and this is publicly available on our website," the spokesman said.

As reported by Fairfax Media, the mine was approved in 2013 to dig five longwalls, each up to two kilometres long, even though it didn't submit a separately commissioned groundwater report until 13 months later.

'Fundamentally flawed'

Dr Turner said consultants Coffer produced reports in October 2012 for 3.4m-high extractions and one a month later for 4.5m.

"The latter matched the mining actually planned and has not been made available and requests for it have been denied," he said. 'It's outrageous that a mining company can withhold information relating to our Special Areas."

The later reports, pro​vided by a different consultancy HydroSimulations, used a different calculation method for drainage zone impacts that is "fundamentally flawed and significantly underestimates the likely height of the drainage zone, by around 50 per cent", Dr Turner said,

(See NPA chart below, interpreting how the drainage zone will be affected with 4m-high longwalls in the Area 3B. Using the Tammetta equation, red dots indicate intersection with the surface, pink ones 0-25m and orange between 25-50m.)

According to Dr Turner, the same flawed method has been used for groundwater assessments at other coal mines in the state, such as Springvale, Moolarben and Narrabri. It is also being used for the mammoth Carmichael coal mine proposed by India's Adani group in Queensland.

NSW Planning downplayed the extent of the water loss at Dendrobium, citing work by independent groundwater expert Col Mackie, who estimated it amounted to 2.33 million litres a day, or 830 ML a year.

"By comparison, Sydney's catchment dams hold over 2.3 million megalitres, and it is estimated that 420,000 megalitres is lost each year in evaporation and environmental flows from the catchment," the spokeswoman said.

Dr Turner said the government had yet to make public Dr Mackie's calculations. Given the rainfall-dependent average daily inflow into Dendrobium is about 8 ML a day, the loss of 2.3 ML amounts to about 29 per cent of the water entering the mine is being lost from storages.

Risk taking

Adam Searle, Labor's mining spokesman, said the government should not be taking risks with the catchment.

"No approvals should be given when the impact on water is unclear, especially in the Special Areas," Mr Searle said. "To do so would be negligence of the highest order, and would constitute serious regulatory failure."

Jeremy Buckingham, Greens energy spokesman, said the government was again cutting corners in its rush to approve new coal projects.

"There are no red lights in the current planning system, so it is no surprise that longwall coal mining is being approved under the Sydney drinking water catchment without a proper understanding of the impact on water and the environment," Mr Buckingham said.

"Longwall coal mining will inevitably fracture the bedrock, drain the swamps and cause irreparable damage and that is why the Greens support a ban on all coal mining [in the catchment]."

Planning, though, said it was applying "a precautionary approach" in only allowing mining to take place in Longwalls 14 and 15, and further approval will be need for numbers 16-18.

"The [Subsidence Management Plan] approval also requires South32 to undertake a comprehensive range of additional subsidence and groundwater monitoring and research, so that the NSW government has all the relevant information available to assess future SMP applications at the Dendrobium mine," the spokeswoman said.

Dr Turner, though, likened the government's approach to feeding Mr Creosote, the grotesquely obese gourmand in "The Meaning Life" who blows up after eating one final "wafer thin" morsel.

"The Department has a well-established record of not taking into proper consideration the accumulating impacts of mining within and around the Special Areas," he said. "The catchment isn't going to suddenly explode, but it is imploding in slow motion."

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